Cracking of hydrocarbon oils



Dec.- 14, 1937.

Original Filed Feb. 26, 1930 2 Sheets-Shed 1 Q 1 (h re/m5 Deb. 14, 1937.1.. c. HUFF 2,102,269

CRACKING OF HYDROCARBON OILS Original Filed Feb. 26, 1930 2 Sheets-Sheet2 7' TOR/YEY Patented Dec. 14, .1937

UNITED STATES PATENT OFFICE CRACKING OF HYDROCARBON OILS ApplicationFebruary 26, 1930, Serial No. 431,405 Renewed April 30, 1935 5 Claims.

This invention relates to the art of treating hydrocarbon oils by themethod of thermal decomposition known as cracking and has for its objectthe production of hydrocarbons, within the boiling range of motor fuel,which are of a highly unsaturated nature and are especially desirablefor use as fuel in internal combustion engines employing highcompression pressures.

With the continually increasing use of high compression internalcombustion engines employing a carbureted fuel the demand for suitablefuel which will withstand the high compression pressures employedwithout appreciable detonation has steadily mounted until such suitablefuel has come to demand considerable premium in the market.

In a cracking process of the liquid-vaporphase type which is in widecommercial use, one of the usual methods of operation is to produce adistillate containing from 60 to 85% more or less, of material fallingWithin the boiling range of gasoline and which is redistilled to efiecta separation of this gasoline-like component. The residual materialcommonly termed pressure distillate bottoms, which is left from thisredistillation of the pressure distillate is exceptionally suitable forthe production of a highly anti-knock motor fuel when processed underhigh temperature or so called vapor-phase cracking conditions. Inasmuchas these so-called pressure distillate bottoms are a highly refractorycracking stock and would considerably lower the throughput if returnedand reprocessed in the liquid vapor-phase system, it would be economicalto treat them separately in a system employing conditions most suitablefor the conversion of this particular oil.

My process comprises a liquid-vapor-phase, system wherein the pressuredistillate vapors are further fractionated in a secondary fractionatingtower within the system and wherein the reflux, corresponding topressure distillate bottoms, from this secondary fractionating' tower isreconverted under vapor phase cracking conditions.

A salient feature of my invention is the optional use of a residuumrevaporizing or flash distilling system wherein the residual productsfrom both the liquid-vapor-phase and the vapor-phase systems may bereleased under reduced pressure and their combined redistillationthereby effected.

My process also provides for the use of reflux from the dephlegmator ofthe flash system, consisting of reflux condensate combined withpreheated and topped raw oil charging stock, as a cooling medium in thevapor-phase dephlegmator or in the liquid-phase dephlegmator, or inboth.

The process also provides for the return of reflux from the dephlegmatorof the vapor-phase system to the liquid-phase heating element and itsreconversion therein.

The attached drawings, Fig. 1 and Fig. 2represent a diagrammaticelevation, not drawn to scale showing one particular construction of anapparatus to which my process is adapted. The raw oil enters the processthrough line I and is fed by means of pump 2 through line 3 and valve linto dephlegmator 58 of the flash system. Here the oil is stripped ofits natural gasoline content, if any, by heat from the vapors arising inthe dephelgmator. The preheated and stripped raw oil together with.reflux condensate from the vapors may collect in the bottom of thedephlegmator 58 and pass therefrom through line 5 and 'valve 5 to thehot feed pump 6. From here the oil may be fed through valve 1, line 8and valve 8 into fractionating tower 42 of the vaporphase system, orthrough valve 9 and line l into the primary dephlegmator 2! of theliquidvapor-phase system or by proper manipulation of the valves 1 and 9any portion may be fed in either direction.

The oil thus fed into the vapor-phase fractionating tower 42 assists incooling and fractionating the vapors arising therein. Its unvaporizedportions are collected together with the reflux condensate in the bottomof the tower and pass through line ll, valve ll, heat exchanger orreboiler l2, through line l2 and valve I3 to pump l3 and is then fed bypump l3 through line 68 and valves 69 and 1 into line IS.

The heat exchanger or reboiler l2 serves to strip the reflux liquid fromfractionating tower d2 of the low boiling gasoline-like constitutentswhich may be contained therein by reboiling the reflux liquid byindirect contact with hot vapors from the vapor-phase reaction chamber39 at the same time partially cooling the cracked vapors. The lowboiling constituents or light ends thus separated may pass through lineH and valve 4' back into the fractionating tower 42 at a point above thereflux level.

Oil fed into the primary dephlegmator 2|I through line I!) serves thesame purpose of assisting cooling and fractionation in this portion ofthe apparatus, collects with other reflux condensate in the bottom ofthis fractionating tower 2| and passes through line l5 and valve IE topump 56. CH from pump I 6 combines in line it with the oil fed from pumpl3 through line 58 and the total combined feed from line, I6 is pumpedthrough the liquid-vapor-phase heating element 11.

This liquid-vapor-phase heating element is located in any suitablefurnacel8. Theoil passing through the heating'element I1 is heated tothe desired temperature under any desired pressure and passes throughline 19 and valve l9 into the liquid-vapor-phase reaction chamber 20.Vapors from this reaction chamber pass through line -68 and valve 68into the primary dephlegmator 2| where they are cooled and fractionatedby ,incoming oil from line I as above described.

Dephlegmator 2| may be any'suitable fractionating device employingany'vsuitable fractionating means such as perforated pans orpacking.

' The vapors leaving primary 'dephlegmator'2 twill consist of a smallamount :ottfixedl gas ,and the product commonly known as pressure idistillate portions of the pressuredistillate whichcorre- T spondtogasoline are separated from the heavier portions. These lighter-portions,may pass as vapor throughline 24,valves 24; and25 into the 7upper; portion of the vapor-phase fractionating tower 42 or they maypass through line 26 controlled by=valve 21 .through condenser 28, line28" and valve 29 into receiver29 wherein theliquid products areseparated from the fixed gas-the flxed'gas-being released through line-30 controlled by valve 3i -and the liquid productsbeing withdrawn tostorage. or elsewhere through line 32:controlled by valve 33.

Reflux; corresponding to what is commonly known as pressure distillate'bottoms, from the secondary fractionating- .tower '23 may passthrough-line 34, valve =34" and by means of pump 35.may:be fed throughvalve 35 and'line 36 to the vapor-phase heating element 35'which islocatedinany suitable furnace 31. This material after being subjected tothe 'desiredconditions of temperature and pressure in heating element 36may pass in ,a-substantiall-y; vaporized state through line '38and'valve :38 and into the vaporphase -reactionchamber 39.-- Vapors fromthis reaction chamber-may pass through line -and valve -=4l to the heatexchanger ,or reboiler 12 .where they reboilthe bottoms from thefractionating tower 42 and "are thereby-partially cooled 'as abovedescribed, and thence continue through line 40 and valve -4I' intothe'vapor-phase fractionating 'tower' 42.

Tower 42 .may takethe form'of'any suitable fractionatingdevice'andispreferably a tower of the-packed or'bubble type. Vaporsleaving this tower pass-through line 43,'valve 43.,conderiser 44,. line44jand 'valve45' into receiver 45 where the condensed'liquid produced isseparatedfrom -the uncondensed gas. The fixed gas is releasedthroughline 46 2controlled by valve 41' and the ,liquid productiswithdrawn to storage or'elsewhere through line '48 controlledby valve49.

The'liquid residual "product from reaction chamber 20:0f theliquid-vapor-phasesystem may .be-"withdrawn by well known means notshown for use as :fuel in thesystem, or to-storage or elsewhere.Theliquid residual product from the reaction chamber 39 of thevapor-phase system may likewise be separately withdrawn by means not'LSh'Own or it may be withdrawn through line '50and valve 5| :into' line'52where it may combine, if desired, with the residual liquid withdrawnfrom reaction chamber 20 through line 53 and valve 54. Either one ofthese residual products or the two combined in any proportion may passthrough line 52 and valve 55, where the pressure is substantiallyreduced, into flash distilling chamber 56. The lighter portions of theresidual liquids are here revaporized by their own latent heat and may*passthrough; line 51 and valve 5? into flash dephlegmator 58.

Flash dephlegmator 58 may be any suitable fractionating device, but ispreferably a tower containing perforated pans or similar fractionatingmeans. The flashed vapors are herein fractionated and partially cooledby incoming 'raw' oil and'the lighter portions of the vapors maypassthrough line 59, valve 59, condenser 60,-,line60' and valve 6| intoreceiver 6| where the condensed liquid is separated from the uncondensedgas; the gas being released through line .62 controlled by valve #63:and condensate 1 being withdrawn through; line 64 controlled by valve65. i 1

The condensed liquid receivers ifl, 45-or. B] may be returned. ;in anyproducts from; any of the desired quantityby wellknownmeans not'shown,

to their respective ,fractionating towers 23," 42

and m assist cooling and: fractionation in the I fractionating towers.The flashedresidual -pr0ductirom flash chamber 56 may be withdrawnthroughlinelifi and valve 61 to l'storage 'or elsewhere. I

Any pressure ranging fromsub-atmospheric to high superatmosphericpressures, say ,up "to 2000 pounds persquare inch-more oriless, may beemployed throughout the system or differential pressures may be employedbetween'various portions of the apparatus. Cracking "temperaturesranging from 700 to ,1400'degrees F. more or less,

may be employed .in eithergor both heating elements butpreferablytemperaturesemployed in heating .element I! are withinftherange of what ;iscommonly termed liquid-phase cracking temperatures,say,700 to, -1000 degrees -F., orthereabouts, and temperaturesemployed'in the heating'element 36 are preferably maintained withinthe'range of what are commonly termed vaporphase cracking temperatures,e. g. 900 to 1400 I degreesF; more or less. I As a specific'example ofone of the many operations possible with my process and 'in the,

apparatus ,just described a 32 :degree A, R I; gravity Mid-Continent gasoil is usedzas charging stock .for the liquid-vapor-phase' process.

The-total charge is fed to the .fractionating zone of-the flashsystemand in combination with the reflux condensateffrom this flashdephlegmat'or is vfed in part to theprimary dephlegmator of theliquid-vapor-phase system and in part 'to the fractionating tower of thevapor-phase system. Reflux condensate and preheated raw oil from both ofthese fractionating zones is subjected in the liquid-vapor-phase heatingelement to. an outlet temperature of approximately 900 degrees F. undera pressure of approximately 225 pounds persquare inch.

Very little liquid is-maintainecl in the reaction chamber of theliquid-vapor-phase system and consequently little or no coke isdepositedin this chamber. Substantially the same pressure is 'maintainedin the chamber 20 and tower 2| as that maintained inthe heating elementI! but this pressure is reduced inthe secondary fractionatingtower of"the liquid-vapor-phase system to approximately 90 poundsper squareinch;

Reflux condensate corresponding to pressure distillate bottoms from thesecondary liquid-vapor-phase fractionating tower comprises the chargingstock to the vapor-phase system. This oil is heated in the vapor-phaseheating element to a temperature of approximately 1200 degrees F., and asubstantially equalized pressure of approximately 80 pounds per squareinch is maintained throughout the vapor-phase system.

Residual oil from both the liquid-vapor-phase and the vapor-phasereaction chambers is flash distilled at a reduced pressure atapproximately 20 pounds per square inch.

Recovery of the various products from an operation such as outlined maybe somewhat as follows:

Approximately 54% of distillate boiling within the range of motor fueland equivalent in antiknock rating to a blend of approximately benzolwith 65% straight run gasoline may be recovered from theliquid-vapor-phase system.

The system in this particular case is so operated that a relatively highpercentage. of pressure distillate bottoms are produced and from thisoil approximately 22% of gasoline based on the charging stock may berecovered by processing in the vapor-phase system. This vapor-phasegasoline while quite possibly of lower gravity than ordinary cracked orstraight run gasoline may still fulfill the boiling range requirementsfor regular or even premium motor fuel and may show a benzol equivalentof some 60% or thereabouts.

About 10% of a relatively heavy distillate is rerovered from the flashsystem and a final heavy residual product from the process removed fromthe flash chamber may represent only 8%, more or less, of the originalcharging stock. The remaining 6% or thereabouts may represent the coke,gas produced and loss in processing.

I claim as my invention:

1. A hydrocarbon oil cracking process which comprises initially crackingthe oil in a primary cracking zone under suflicient pressure to retain asubstantial portion thereof in the liquid phase, separating the thustreated oil into vapors and unvaporized oil, simultaneously cracking acondensate separated from said vapors in the vapor phase in a secondcracking zone, flash distilling said unvaporized oil by pressurereduction and dephlegmating the resultant flashed vapors independentlyof the vapor phase cracked vapors rom said second cracking zone and incontact with fresh charging oil for the process thereby forming amixture of unvaporized charging oil and flash reflux, dephlegmating thevapors from said primary cracking zone and the vapors from said secondcracking zone in contact With portions of said mixture, then supplyingthe charging oil and resultant reflux condensate to the primary crackingzone, and condensing the dephlegmated vapors.

2. A process as defined in claim 1 further characterized in that saidcondensate comprises a secondary reflux condensate produced by secondarydephlegmation of the vapors from said primary cracking zone.

3. A hydrocarbon oil cracking process which comprises initially crackingthe oil in a primary cracking zone under sufl'lcient pressure to retaina substantial portion thereof in the liquid phase, separating the thustreated oil into vapors and unvaporized oil, simultaneously cracking acondensate separated from said vapors in the vapor phase in a secondcracking zone, flash distilling said unvaporized oil by pressurereduction and dephlegmating the resultant flashed vapors in contactwith. fresh charging oil for the process thereby forming a mixture ofunvaporized char ing oil and flash reflux, passing the vapors from saidprimary and second cracking zones to independent dephlegmating zones,dividing said mixture and introducing a portion thereof into each ofsaid independent dephlegmating zones to serve as a dephlegmating mediumtherein, supplying unvaporized charging oil and reflux condensate fromsaid dephlegmating zones to the primary cracking zone, and condensingthe vapors unconolensed in said dephlegmation.

4. A hydrocarbon oil conversion process which comprises crackinghydrocarbon oil in a primary cracking Zone under suflicient pressure toretain a substantial portion thereof in liquid phase, separatelyremoving vapors and unvaporized oil from said zone, fractionating theVapors to form a relatively heavy reflux condensate and a lighter refluxcondensate, returning such heavy reflux condensate to said zone,cracking the lighter reflux condensate substantially in vapor phasein asecond cracking zone maintained at higher temperature than said primaryzone, fractionating the resultant vapor phase cracked vapors, reducingthe pressure on the unvaporized oil withdrawn from said primary zone andthereby flash distilling the same, fractionating resultant flashedvapors independently of said vapor phase cracked vapors thereby formingflash reflux condensate, introducing such flash condensate into contactwith the vaporphase cracked vapors undergoing fractionation andsupplying resultant liquid products to the primary cracking zone, andfinally condensing the fractionated vapors.

5. A conversion process which comprises cracking hydrocarbon oil in aprimary cracking zone under suflicient pressure to retain a substantialportion thereof in liquid phase, simultaneously cracking a lighter oilsubstantially in vapor phase in a second cracking zone maintained athigher temperature than said primary zone, fractionating resultant vaporphase cracked vapors to condense heavier fractions thereof, removingunvaporized oil from said primary zone and flash distilling the same bypressure reduction, fractionating resultant flashed vapors independentlyof said vapor phase cracked vapors, introducing flash reflux thus formedinto contact with said vapor phase cracked vapors undergoingfractionation and supplying liquid products of this fractionating stepto said primary zone, removing vapors from the primary zone andfractionating the same independently of said vaper phase cracked vapors,supplying resultant reflux condensate to the second cracking zone assaid lighter oil, and finally condensing the fractionated vapors.

LYMAN C. I-IUFF.

